Method of preparation of coupled branched and linear polymer compositions

ABSTRACT

A continuous process for manufacture of a polymer including branched and linear components comprising first polymerizing conjugated diene(s) in the presence of an organometallic initiator to a conversion that is at least 90% complete. A coupling agent is added to obtain a polymer including branched and linear components. The coupling agent is added at a ratio of about 0.3 to about 0.6 coupling equivalents to initiator equivalents.

This application is a divisional of U.S. Ser. No. 09/533,746, filed Mar.23, 2000, now U.S. Pat. No. 6,525,140.

BACKGROUND OF THE INVENTION

Polymers and copolymers of conjugated dienes such as polybutadiene,polyisoprene and styrene-butadiene rubbers possess physical propertieswhich make them suitable for many important applications such assynthetic rubbers and as additives to other polymeric systems such as,for example, high impact polystyrene (HIPS). Moreover, HIPS can bemanufactured by polymerization of styrene in the presence of 5-10%dissolved polybutadiene or butadiene copolymer rubber. Early in thepolymerization, phase separation begins because of the immiscibility ofthe rubber within the polystyrene being formed and the depletion of thestyrene phase. Grafting of polybutadiene with the polystyrene then takesplace. Toughness, as well as other mechanical and rheological propertiesof HIPS, is strongly affected by the nature of the rubber phase. In thisregard, some of the characteristics of the rubber which may be modifiedto control the overall HIPS performance include concentration, volume,particle size, grafting and cross-linking ability, molecular weight, andviscosity.

One focus of the present invention is use of polybutadiene as anadditive in HIPS or ABS resins. Specifically, the present inventionaddresses the desire that the polybutadiene additive have usefulmolecular weight and viscosity ranges. In this regard, strictly linearpolybutadiene of low molecular weight typically has a low Mooneyviscosity, making the polybutadiene difficult to handle, while atetra-coupled version of the same low molecular weight polymer is toohigh to be processed. One mechanism to achieve a desired molecularweight and viscosity is to use a blend of tetra-coupled and linearpolymer chains.

One method for the manufacture of copolymers having linear and branchedsegments rubbery composition includes a blend of from 40-94 parts byweight (pbw) Component A and from 60-66 pbw of Component B. Component Aincludes a rubbery (co)polymer(s) of conjugated dienes, and at least 60%by weight of the components in the A portion are branched polymers.Component B is generally the same as Component A, but consists of linear(co)polymer(s). The process of manufacture involves forming Component Ain a first step, Component B in a second step and performing a thirdstep of blending A and B.

Another process is directed to polymerizing at least one diene monomerto a conversion between 30 and 70% to produce low molecular polydienechains; joining from 20 to 70% of those chains with a suitable branchingagent; and allowing the polymerization to continue to produce apolydiene rubber blend. However, by failing to perform sufficientconversion in the first step, insufficient solution viscosity isproduced.

BRIEF SUMMARY OF THE INVENTION

In an exemplary embodiment of the invention, a continuous process forthe manufacture of a polymer composition is disclosed. Particularly, theprocess is directed to the manufacture of a polymer including branchedand linear segments by polymerizing diene monomers in the presence of anorganolithium initiator of the general formula MR_(x) to at least 90%,preferably 99% conversion, to produce polydiene chains. Thereafter, acoupling agent is added to obtain a polymer of mixed branched and linearpolydiene units. The coupling agent is added at a ratio of about 0.3 toabout 0.6 equivalents to organometallic initiator equivalents. Theresulting polymer mixture has a solution viscosity in the range of about150 to 190 cP (0.15 kg/m.s+0.19 kg/m.s) and a Mooney viscosity in therange of about 60 to 85 (ML4).

The process advantageously produces a mixture of linear and branchedpolymers, thereby gaining the benefits of the individual polymerswithout requiring separate production segments to make the individualproducts. Moreover, the process is performed continuously, not requiringseparate polymerization stages and a subsequent blending of components.The present invention limits the coupled polymer percentage in theoverall mixture to produce a high molecular weight fraction that wouldotherwise would be difficult to process by itself. The resultant polymeris particularly suited for use as an additive in the manufacture of HIPSand ABS resins.

DETAILED DESCRIPTION OF THE INVENTION

Feed stocks usually include one or more conjugated diolefin monomers.Typically, the feedstock is an admixture of the conjugated diolefin withother low molecular weight hydrocarbons. Such admixtures, termed lowconcentration diene streams, are obtained from a variety of refineryproduct streams, such as naptha-cracking operations.

Preferred diene monomers utilized in the preparation of the linearpolydiene chains normally contain from 4 to 12 carbon atoms, with thosecontaining from 4 to 8 carbon atoms being most commonly used.1,3-butadiene and isoprene are the most common conjugated diolefinmonomers used in this process. Additional monomers that can be utilizedinclude 1,3-pentadiene, 2-methyl-1,3-pentadiene, 4-butyl-1,3-pentadiene,1,3-hexadiene, 1,3-octadiene, 2,3-dimethyl-1,3-butadiene, piperylene,2,3-dibutyl-1,3-pentadiene, 2-ethyl-1,3-pentadiene,2-ethyl-1,3-butadiene, 3-butyl-1,3-octadiene, 2-phenyl-1,3-butadiene,styrene and the like, alone or in admixture. Some typical examples oflow molecular weight hydrocarbons which may be admixed with the monomersin the polymerization feed include propane, propylene, isobutane,n-butane, 1-butene, isobutylene, trans-2-butene, cis-2-butene,vinylacetylene, cyclohexane, ethylene, propylene, hexane, heptane,octane and the like.

Polydiene rubbers which are copolymers or terpolymers of diolefinmonomers with one or more other ethylenically unsaturated monomers canalso be prepared from the process of this invention. Some representativeexamples of ethylenically unsaturated monomers that can potentially besynthesized into such polymers include vinylidene monomers; vinylaromatics such as styrene, α-methylstyrene, bromostyrene, chlorostyrene,fluorostyrene and the like; α-olefins such as ethylene, propylene,1-butene, and the like; vinyl halides, such as vinylbromide,chloroethane (vinylchloride), vinylfluoride, vinyliodide,1,2-dibromethene, 1,1-dichloroethane (vinylidene chloride),1,2-dichloroethane, and the like; vinyl esters, such as vinyl acetate;α,β-olefinically unsaturated nitriles, such as acrylonitrile anides,such as (meth)acrylamide, N-methyl acrylamide, N,N-dimethylacrylamide,methacrylamide and the like.

The polymerization of the present invention is normally carried out in ahydrocarbon solvent which can be one or more aromatic, paraffinic orcycloparaffinic compounds. The solvents normally contain from 4 to 10carbon atoms per molecule and are liquids under the polymerizationconditions. Some representative examples of potentially useful organicsolvents include pentane, cyclohexane, normal hexane, benzene, toluene,xylene, ethyl benzene, and the like, alone or in admixture. In solutionpolymerizations which utilize the process of this invention, thepolymerization medium normally can include 5 to 35 weight percentconjugated diolefin monomers. The polymerization medium preferablycontain from 10 to 30 weight percent monomers, more preferably 20 to 25weight percent monomers.

Accordingly, the polymerization medium includes an organic solvent,reactant monomers, and at least one initiator selected fromorganometallic compounds of the general formula M(R)_(x) wherein M isGroup I or Group II metal and R is an organic group described hereinbelow. Organometallic initiators include the monofunctional andmultifunctional types known for polymerizing the monomers describedherein. Generally, utilization of a monofunctional organometallicinitiator may be preferable. Preferred metals include lithium,potassium, sodium, zinc, magnesium, and aluminum. Of these, theorganolithium initiators are particularly preferred.

The term “organolithium compounds”, as employed herein, refers toorganolithium compounds which correspond to the formula RLi, wherein Ris a C₁-C₂₀ hydrocarbyl radical, preferably C₃-C₆, advantageously analiphatic radical, but also may be C₆-C₂₀ cycloaliphatic or aromatic,preferably C₆-C₁₂. Preferred RLi compounds are n-butyl and sec-butyllithium. Other suitable RLi compounds include but are not restricted tothose in which the R groups are ethyl, n-propyl, isopropyl, n-arnyl,sec-amyl, sec-hexyl, n-hexyl, n-heptyl, octyl, nonyl, decyl, dodecyl,octadecyl, phenyl, tolyl, dimethyl/phenyl, ethylphenyl, naphthyl,cyclohexyl, methylcyclohexyl, ethylcyclohexyl, cycloheptyl, allyl,2-butenyl, 2-methyl butenyl, cyclopentylmethyl, methycyclopentylethyl,pohenylethyl, cyclopentadienyl, naphthyl, penylcyclohexyl, and the like.

The amount of organometallic initiator utilized can vary with themonomers being polymerized and with the molecular weight desired for theresultant polymer. However, as a general rule, from 0.01 to 1 phm (partsper 100 pbw of monomer) of initiator will be utilized. In most cases,0.025 to 0.07 phm of the organometallic initiator may be preferred.

The polymerization temperature can vary over a broad range from about−20° to 150° C. In most cases, a temperature within the range of about30° to 120° C. can be useful. The pressure used will normally besufficient to maintain the substantially liquid phase under theconditions of the polymerization reaction.

The polymerization reaction is generally conducted for a time sufficientto obtain a conversion of at least about 90% and preferably at least 99%conversion. More specifically, the polymerization is preferably carriedout until at least 90% of the charged monomer has been polymerized.Accordingly, using 1,3 butadiene feedstock and the preferred range ofinitiator, the first stage of the process typically yields polybutadienehaving a weight average molecular weight (M_(w)) in the range of about70,000 to 250,000.

Thereafter, a coupling agent can be added to obtain the preferredmixture of linear and branched polydiene units. While many couplingagents are known in the art and may be applicable to the presentinvention, the multifunctional coupling agent preferably joins at leastthree polydiene chains. Representative examples of suitable couplingagents include multi-vinyl aromatic compounds, multi-epoxides,multi-isocyanates, multi-amines, multi-aldehydes, multi-ketones,multi-halides, multi-anhydrides, multi-esters and the like. Preferredcoupling agents include multi-halides such as SiCl₄, SiBr₄, and SiI₄. Inaddition to these silicon multihalides, other metal multihalides,particularly, those from tin, lead, or germanium also can be readilyemployed as the coupling branching agent. Preferred among these areSnCl₃, hexachloraldisilane, methyl trichlorosilane, CCl₄, and trichloromethyl silane. The reaction can be terminated by any known method suchas the addition of water, lower alcohols, etc.

Coupling agent can be added in a ratio of about 0.2 to 0.8 couplingequivalents to initiator equivalents. More preferably, the ratio can beabout 0.3 to about 0.6 equivalents of coupling agent to organometallicinitiator.

In this manner, the desired ratio of linear units to branched units canbe achieved to provide a polybutadiene polymer having a solutionviscosity in the range of 100 to 300 cP (0.10 to 0.30 kg/m.s) and Mooneyviscosity in the range of 30 to 120 (ML4). A weight average M_(w) ofbetween about 150,000 and about 350,000, preferably from about 225,000to about 275,000 can be obtained.

As recognized by the skilled artisan, a variety of modifications and/oradditions to the basic process of this invention can be made withoutdeparting from the intention thereof. For example, various modifiersstabilizers and antioxidants may be employed.

To illustrate the instant invention, the following exemplary embodimentis provided. However, the embodiment is for the purpose of illustrationonly and the invention is not to be regarded as limited to the specificmaterials or conditions illustrated in the following examples.

The system was first flushed and dried. Into a first mixing tank werecombined approximately 285 phm hexane, approximately 100 phm 1,3butadiene, approximately 0.02 phm 1,2-butadiene, a titrating agent andvinyl modifier. This blended mixture was transferred to a secondreaction tank and approximately 0.067 phm butyllithium catalyst wasadded. The reaction raised the temperature to approximately 200-220° F.(93.3-104.4° C.) and proceeded until approximately greater than 98%monomer conversion was completed. The resultant polybutadiene wastransferred to a third mixing tank to which approximately 0.02 phm SiCl₄was added (SiCl₄/Li=0.45Cl/Li; coupling agent to initiator equivalents).A stabilizer was added and the reaction terminated via the addition ofwater. The resultant product was dried and baled. The polybutadiene hada solution viscosity of about 170 cP (0.170, k/m.s), a Mooney viscosityof about 65 (ML4) and a M_(w) of 260,000. Accordingly, mixed coupled andlinear polybutadiene having the desired characteristics can be preparedvia the inventive process.

While certain representative embodiments and details have been shown forpurposes of illustrating the present invention, various modificationsand changes to the process can be made without departing from the scopeof the present invention.

1. A polymer prepared by polymerizing at least one conjugated diene inthe presence of an organometallic initiator comprised of an organicgroup and a Group I or Group II metal, to a conversion that is at least90% complete and adding a coupling agent to produce a polymer comprisedof branched and linear chains, said coupling agent being added at aratio of about 0.3 to about 0.6 coupling agent equivalents to initiatorequivalents, said polymer having a Mooney viscosity in the range ofabout 60 and 85 (ML4).
 2. The polymer of claim 1 having a weight averagemolecular weight between about 225,000 and about 275,000.
 3. The polymerof claim 1 having a solution viscosity in the range of about 150 to 190cP (0.15 to 0.19 kg/m.s).
 4. The polymer of claim 1 wherein said atleast one conjugated diene monomer comprises 1,3-butadiene.
 5. Thepolymer of claim 1 wherein said coupling agent comprises silicontetrachloride.
 6. The polymer of claim 1 wherein said organometallicinitiator comprises n-butyl-lithium.
 7. The polymer of claim 1 whereinfrom about 0.01 to 1.0 phm of organometallic initiator is used.
 8. Thepolymer of claim 1 wherein said polymer has a weight average molecularweight between about 150,000 and about 350,000.
 9. The polymer of claim1 further including the addition of a vinyl modifier to saidpolymerization.
 10. The polymer of claim 9 wherein said vinyl modifiercomprising 1,2-butadiene.